Short answer: the Sony IER-EX15C. It ranks #981 of 1291 in-ear headphones by sound quality, rated 3.1/5, at $28; the KZ ZEX ranks #1034, rated 2.8/5, and costs $28.99, so there is little reason to consider the other one.
The Sony IER-EX15C is the better-sounding pick. At 0 lbs (3 g) per earpiece it is very light, and the built-in microphone makes it handy for calls. The catch: Sub-bass rolls off about 2.8 dB below target under 60 Hz, so deep synth bass and rumble are subdued.
Why pick the KZ ZEX: It pairs a 10mm dynamic driver with a 6.8mm electrostatic driver at a low price, and its 25 ohm load suits phones and dongles. The catch: Across 16 hobbyist measurements a 7.4 dB dip near 3.3 kHz pushes vocals back and a 6.1 dB peak near 10.2 kHz adds sizzle to cymbals, while sub-bass sits about 3.7 dB below target under 60 Hz.
Buy the Sony IER-EX15C. It is rated higher for sound quality than the KZ ZEX and costs less, so it is the default pick unless a specific strength of the other one matters more to you.
Still deciding? The full Headphones rankings cover every ranked option.
At 3 g per earpiece it is very light, and the built-in microphone makes it handy for calls.
Amazon $28.00 eBay
It pairs a 10mm dynamic driver with a 6.8mm electrostatic driver at a low price, and its 25 ohm load suits phones and dongles.
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Specifications Side By Side
| Sony IER-EX15C | KZ ZEX | |
|---|---|---|
| Price | $28.00 | $28.99 |
| Ranked | #981 of 1291 in In-Ear Headphones | #1034 of 1291 in In-Ear Headphones |
| Form Factor | In-ear | In-ear |
| Back | Closed | Closed |
| Harman Preference Score | 62 (median of 2 squig.link measurements, calibrated to AutoEQ) | 59 (measured by crinacle, via AutoEQ) |
| Deviation From Target | 2.85 dB standard deviation | 3.54 dB standard deviation |
| Tonal Tilt | -0.43 (negative is warmer, positive brighter) | -0.09 (negative is warmer, positive brighter) |
| Sub-bass Extension | Within 6 dB of target down to 20 Hz (-5.0 dB at 30 Hz) | Within 6 dB of target down to 20 Hz (-4.7 dB at 30 Hz) |
| Connection | Wired | Wired |
| Drivers | 1 x 5mm | 1 x 10mm dynamic + 1 x 6.8mm electrostatic |
| Weight | 0 lbs (3 g) per earpiece | - |
| Frequency Response | 20Hz - 20kHz (Manufacturer specified) | 20Hz - 40kHz (Manufacturer specified) |
| Built-in Microphone | Yes | - |
| Driver Type | - | Hybrid (1 dynamic + 1 electrostatic) |
| Impedance | - | 25 ohms |
| Sensitivity | - | 103 dB |
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